Giải thích các bước giải:
$\begin{array}{l}
\left\{ \begin{array}{l}
x + z = 3t\\
x - z = - 4 - t
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
\left( {x - z} \right) + \left( {x + z} \right) = - 4 - t + 3t\\
\left( {x + z} \right) - \left( {x - z} \right) = 3t - \left( { - 4 - t} \right)
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
2x = - 4 + 2t\\
2z = 4t + 4
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x = - 2 + t\\
z = 2t + 2
\end{array} \right.
\end{array}$
